1. Field of the Invention
This invention relates to anti-skid compositions and is particularly related to an anti-skid composition and method for coating structural panel board and other substrates in order to impart slip resistance thereto. 2. Description of the Prior Art
Plywood is widely used in the construction industry and has been the material traditionally used to sheath sloping roof decks. Plywood, however, is costly and therefore efforts have been made to replace plywood with Waferboard, the trade name for a less expensive structural panel board composed of wood flakes, phenol-formaldehyde resin and slack wax.
Waferboard is generally composed of wafers or flakes of wood, poplar being preferred, of about 0.020 inches to 0.080 inches thick, about 2 inches long and about 2 inches wide. The wafers are bonded together with a waterproof adhesive, such as an isocyanate or phenol formaldehyde, wherein the adhesive solids can vary from about 1 to 5 weight percent of the wood flakes. Waferboard or panel board also generally includes about 0.25 to 0.75 weight percent wax solids to enhance its water repellency.
However, waferboard suffers from inherent disadvantages compared to plywood for roofing applications. When wet, a condition that would be frequently encountered on rooftops exposed to rain, waferboard exhibits a very low coefficient of friction. Consequently, there is an increased danger of slippage to materials and personnel working on sloped roofs which are sheathed with waferboard. Waferboard has a coefficient of friction of about 0.415.
Coefficient of friction (.mu.) is defined as ratio of the force (F) required to move one surface over another to the total force (W) pressing the two surfaces together in the following relationship: ##EQU1##
Although plywood is more expensive than waferboard, it has a much higher surface coefficient of friction and thus does not have the disadvantages of waferboard. Consequently, waferboard has not been heretofore successful in replacing plywood as a material in roof construction.
Efforts to improve the surface coefficient of friction of waferboard have included texturing its surface by using screens and embossed cauls during its manufacture. However, this technique is cumbersome and has not resulted in significant increases in the surface coefficient of friction of the waferboard.
Various anti-skid compositions have been suggested for coating plywood and other structural materials in order to impart slip resistance thereto. For example, U.S. Pat. No. 3,527,146 to Garling discloses a non-skid coating composition which comprises a bonding composition and an aggregate. The aggregate is an elastomeric polymer such as ground vulcanized rubber and can include such ingredients as iron oxide pigment, titanium dioxide and fine silica. Numerous resins are disclosed as the bonding composition, such as various phenol-formaldehyde resins used with urea, and polyvinyl acetate as an aqueous emulsion vehicle.
U.S. Pat. No. 3,598,677 to Bergmeister discloses a method of preventing slippage amongst stacked packages of paper, cardboard and the like by providing a anti-slip adhesive comprising an aqueous dispersion of an adhesive olefinic compound in admixture with inorganic or organic pigments. An aqueous dispersion of polyvinyl acetate is disclosed as an anti-slip adhesive, and wood flour or peanut shell flour are disclosed as fillers for the pigment.
U.S. Pat. No. 2,789,098 to Collinson discloses a resin composition having "non-crazing" characteristics by including furfuraldehyde as a non-crazing agent in the formulation. The composition also includes various nut shell flours such as walnut shell, peanut shell an the like as a cellulose filler, and furfuraldehyde and urea-formaldehyde as an adhesive. Ammonium chloride solution may also be included in the composition as a catalyst.
Chemical Abstracts, Volume 93, No. 244361e, page 310, (1980) discloses that roofing tile supporting materials from plywood or particle board rubbed with coarse abrasive paper and coated with a mixture containing urea resin, ferric oxide, wax emulsion and ammonium chloride, and heated at 80.degree. C. for 10 minutes produces excellent slip-resistant tiles.
Other patents of interest include U.S. Pat. No. 3,681,274 to Oetgen et.al., U.S. Pat. No. 2,873,260 to Corwin, U.S. Pat. No. 3,100,754 to Booth et.al., U.S. Patent No. 2,440,789 to Van der Pyl, and U.S. Pat. No. 2,601,598 to Daniel, Jr.